Magnetic disc drive storage devices store digital data on rotatable magnetizable disc surfaces. Data are written to and read from concentric tracks on the disc surface by read and write transducers, usually called “heads”, that are carried on the slider. Each slider is mounted to a flexible suspension that is supported by an actuator arm of an actuator member, such as an E-block. The actuator member is rotated by a voice coil actuator motor to move the slider and head along an arcuate path that is oriented generally radially across the disc. The head is positioned relative to a selected track on the confronting disc by moving the slider along its arcuate path defined by the rotating actuator member.
The disc drags air along its surface in a generally circular pattern around its axis as it rotates. The slider body includes an air bearing surface (ABS) that reacts against the air dragged beneath the ABS by the disc. The airflow develops a lifting force to lift the slider and “fly” it and the head above the disc surface. The flexible suspension supports the slider to the actuator arm and biases the slider against the lifting force of the airflow to maintain a predetermined fly height of the slider adjacent the disc surface.
As the slider moves along its arcuate path generally radially across the disc, its skew changes relative to the circular tracks on the disc between a positive orientation at outer radial tracks and a negative orientation at inner radial tracks. The circular airflow confronts the slider approximately tangentially to the track, so the direction of airflow impinging the slider changes with the skew of the slider. Consequently, the airflow impinging the slider is from a different direction for different skew orientations of the slider. More particularly, the airflow impinges the leading surface (edge) and one or the other side surfaces (edges) of the slider, depending on whether the slider is in a positive or a negative skew orientation.
At a zero skew orientation (where the airflow impinges the leading surface at 90°), any vortices shed from the slider are captured in the wake following the trailing surface. The pattern of vortices is usually symmetrical relative to the slider. However at non-zero skew orientations (either positive or negative skew), the pattern of shed vortices is not symmetrical, leading to asymmetrical off-track forces on the slider that tend to shift the slider radially. If these asymmetrical off-track forces are at the structural mode of the suspension, they may cause non-repeatable runout (NRRO) in the form of radial vibration in the slider and suspension.
As the need increases for disc drives with increased disc data density and performance, a corresponding need arises for increasing track density and media speed. Increasing track density requires reduction of the widths of tracks and spacing between them across the disc radius. Narrower tracks, smaller track spacing and increased media speed all contribute to increasing the need for more precise track following techniques, and particularly to minimizing off-track forces that affect the slider radial position. The present invention provides a solution to this and other problems, and offers other advantages over the prior art.